1. Field of the Invention
The present invention relates to a high efficiency xe2x80x9chigh sidexe2x80x9d circuit.
2. Discussion of the Related Art
Different circuit configurations are known wherein a DMOS transistor can work as a switch. One configuration among these configurations is that wherein the drain terminal of the DMOS is connected to high voltages, as the supply voltage, while the source terminal is connected to a load which has the other terminal connected to ground; such circuit configuration is called xe2x80x9chigh sidexe2x80x9d. This circuit is utilized in numerous appliances as in engine control circuits or regulators, in order to drive different loads, but, particularly, inductive loads.
A typical high side circuit configuration, shown in FIG. 1, includes a DMOS transistor 1 which has the drain D connected to a supply voltage Vcc and the source S connected both to the cathode of a diode D1, and to a terminal of an inductive load 2 including an inductance L and a resistance R. Both the anode of the diode D1 and the other terminal of the inductive load 2 are connected to ground. The gate terminal G of the DMOS transistor 1 is connected both to a terminal of a current generator 1 and to a terminal of a switch S0, which can be formed by a MOS or DMOS transistor and has the other terminal connected to ground. The second terminal of the current generator 1 is connected to a voltage Vboot (produced generally by a charge pump) which is higher than the supply voltage Vcc in order to drive the DMOS 1 in a resistive way.
With the switch S0 open the gate terminal G of the DMOS 1 is connected to the voltage Vboot in order to turn on the transistor 1 allowing the current flow into the load 2. Closing the switch S0 the gate terminal of the DMOS 1 is connected to ground in order to turn off the transistor 1. In this way the inductance L is demagnetized through the diode D1 and the capacitance at the gate G of the DMOS is discharged to ground.
The aforementioned high side circuit has numerous problems.
First, the switch S0 must be dimensioned so as to withstand the voltage Vboot, which is a voltage much higher than the supply voltage Vcc.
With the decrease in the lithography of the technologies to produce DMOS transistors and also with the reduction of the gate oxide thickness, the threshold voltage of the DMOS transistors is notably reduced so that it is actually equal or lower than 1 V. The source terminal S of the DMOS 1 by the current re-circle, with the transistor turned off, can be carried to a negative voltage which can cause the non-desired turning on of the transistor 1 and a non-controlled current peak which can damage the transistor 1 and cause an efficiency loss.
Also, in the aforementioned circuit, it is provided that the charge stored in the gate G is discharged to ground rather that into the load thereby causing a further efficiency loss of the circuit.
In view of the state of the art described, it is an object of the present invention to provide a xe2x80x9chigh sidexe2x80x9d circuit which has a higher efficiency than the known circuits and solves at least the aforementioned problems.
According to the present invention, this and other objects are attained by a high side circuit comprising at least one power device having a first non-drivable terminal connected to a supply voltage, at least one load connected between a second non-drivable terminal of the power device and ground, driving circuitry comprising transistors which are connected to each other and to a higher voltage than said supply voltage in order to control the turning on and the turning off of the power device and to reduce or minimize the potential difference between the second non-drivable terminal and a drivable terminal of the power device during the turning off state to avoid the re-turning on of the same power device.
As a result of the present invention it is possible to form a xe2x80x9chigh sidexe2x80x9d circuit which, as a result of a different driving circuitry of the DMOS transistor, assures high efficiency of the high side circuit in any operating state.